Secondary alkoxyalkanoic acids are useful as anionic detergents. These acids, being composed of only the elements C, H and O, do not pose the environmental problems that other detergents containing heteroatoms such as N, S, and P pose. The alkoxyalkanoic acids can be prepared in a three-step process by first reacting a secondary alkanol with ethylene oxide and an acid catalyst, then reacting the resultant seed alkoxylate with an alkaline catalyst and ethylene oxide and thereafter converting the secondary alkoxyalkanol to an alkoxyalkanoic acid.
Japanese Patent No. 50-96516, issued Jul. 31, 1975, discloses a process for the preparation of carboxylic acid salts by the liquid phase dehydrogenation of alcohols with caustic alkali in the presence of precious metal catalysts, including palladium. This process uses a relatively high temperature, 100.degree. C. -270.degree. C. These high temperatures can degrade the ether linkages especially in the highly ethoxylated alcohols.
It is known to use nitroxyl radicals/oxoammonium salts in the oxidation of primary alcohols to produce aldehydes and acids and secondary alcohols to ketones. Journal of Organic Chemistry, vol. 52 (12), pp. 2559-2562; Pure and Applied Chemistry, vol. 62(2), 1990, pp. 217-222; Journal of Organic Chemistry, vol. 55, 1990, pp. 462-466. The primary products produced in these processes are aldehydes and the stoichiometrically consumed oxidant is hypochlorite.
It is generally more difficult to oxidize secondary alkoxyalkanols than alkanols or primary alkoxyalkanols as it is difficult to oxidize secondary alkoxyalkanols without splitting the molecular chain at the ether linkage at the secondary carbon and thereby producing a large proportion of undesired by-products. Secondary alkoxyalkanols are much prone to this cleavage reaction relative to primary alkoxyalkanols due to the greater lability of the secondary versus primary ether linkage.
It is therefore an object of this invention to produce secondary alkoxyalkanoic acids in high yields and with high selectivities from secondary alkoxyalkanols without producing large amounts of other products such as olefins and polyethylene glycols.
It is a further object of this invention to provide a process for the preparation of secondary alkoxyalkanoic acids in which highly corrosive, difficult to separate, side-products are not formed.
It has been found that secondary alkoxyalkanoic acids can be produced in high yields and with high selectivities by using catalytic amounts of a stable free radical nitroxide, a NO.sub.x -generating compound and an oxidant.